This invention relates to a fluid jet loom in which the supply of a jet fluid used for insertion or the weft yarn into the warp shed, such as air or water, is controlled by a valve unit or valve units. More particularly, this invention relates to a method and an apparatus for monitoring the weft insertion in such loom.
In air jet looms, the weft yarn ejected from the weft yarn inserting main nozzle is introduced into a weft yarn guide passage defined by a so-called modified reed or a large number of weft yarn guide members juxtaposed on the slay. A plurality of auxiliary nozzles are provided along the guide passage to help the weft yarn to complete its travel or flight along the guide passage. The state of travel of the weft yarn being inserted in this manner is governed by tne weft inserting conditions such as fluid jet pressure or timing from the main or auxiliary nozzles. Unless these weft inserting conditions are controlled satisfactorily, such weft inserting error as the weft yarn deviating from the weft yarn guide passage or forming a loop in the guide passage during weft insertion will not be avoided, thus detracting considerably from the quality of the woven fabric.
Therefore, the timing of fluid ejection at the main or auxiliary nozzles need be controlled in accordance with the prevailing weaving conditions such as the kind of the weft yarn or the cloth width. Such control can be made by adjustment of the timing of opening or closing the valve units used for controlling the supply of the jet fluid to the respective nozzles. Such valve timing adjustment is done while checking the fluid pressure at the injection nozzle. For example, as disclosed in the Japanese laid-open Utility Model Publication No. 87372/1980, the foremost part of a connection tube from an air pressure gauge is sealingly connected to an ejection orifice of the auxiliary nozzle, and the valve opening timing is adjusted in such a manner that the pressure indicated on the gauge rises to the peak state at the loom rotation angle corresponding to the predetermined ejection start time at the auxiliary nozzle.
However, since such opening timing adjustment may be achieved while the loom is at a standstill it is not possible to make a check as to whether the fluid discharge is taking place in the preset manner during tne actual loom operation. Thus, when one of the valve units is used for controlling the fluid ejection at an auxiliary nozzle during the loom operation, the number of weft insertion errors may be increased drastically.
Such failure of the valve unit may be caused for example when the start signal for the magnetic solenoid is missing, or when a noise signal other than tne start signal is occasionally applied to cause the malfunction of the solenoid. In addition, the sliding valve piston may be burned resulting in an increased frictional resistance thus oostructing the smooth valve opening or closing operation. In a mechanical valve unit in which the valve is moved by a cam in the forward stroke and by a spring in the rearward stroke, there may be instances wherein, on account of the burned state of the valve piston, the spring force is not effective to cause the return movement of the valve piston.
However, it is difficult and time-consuming to deduce from the apparent increase in the number of weft inserting errors that the cause of trouble resides in the malfunction of the valve unit or units.
When the air pressure gauge is used for adjustment of the nozzle opening timing as mentioned hereinabove, the ejection port of the auxiliary nozzle is stopped by tne foremost part of the auxiliary nozzle so that the discharge fluid pressure in the auxiliary nozzle reaches a maximum in a snort time irrespective of the opening degree of the valve piston. Thus, the adjustment of the valve opening timing based on the peak indication on the pressure gauge is extremely difficult and requires great skill on the part of the operator.
Therefore, there are presently desired a method and an apparatus for easily and precisely sensing the actual fluid ejection timing during the loom operation and monitoring the weft insertion for assuring the optimum weft inserting conditions.